Buggy code:
public class FileSystemUtils { private static final FileSystemUtils INSTANCE = new FileSystemUtils ( ) ; private static final int INIT_PROBLEM = - 1 ; private static final int OTHER = 0 ; private static final int WINDOWS = 1 ; private static final int UNIX = 2 ; private static final int POSIX_UNIX = 3 ; private static final int OS ; private static final String DF ; public FileSystemUtils ( ) { } @ Deprecated public static long freeSpace ( final String path ) throws IOException { } public static long freeSpaceKb ( final String path ) throws IOException { } public static long freeSpaceKb ( final String path , final long timeout ) throws IOException { } public static long freeSpaceKb ( ) throws IOException { } public static long freeSpaceKb ( final long timeout ) throws IOException { } long freeSpaceOS ( final String path , final int os , final boolean kb , final long timeout ) throws IOException { } long freeSpaceWindows ( String path , final long timeout ) throws IOException { } long parseDir ( final String line , final String path ) throws IOException { } long freeSpaceUnix ( final String path , final boolean kb , final boolean posix , final long timeout ) throws IOException { <START_BUG> if ( ( path . length ( ) ) == 0 ) { <END_BUG> throw new IllegalArgumentException ( "Path<seq2seq4repair_space>must<seq2seq4repair_space>not<seq2seq4repair_space>be<seq2seq4repair_space>empty" ) ; } String flags = "-" ; if ( kb ) { flags += "k" ; } if ( posix ) { flags += "P" ; } final String [ ] cmdAttribs = ( ( flags . length ( ) ) > 1 ) ? new String [ ] { FileSystemUtils . DF , flags , path } : new String [ ] { FileSystemUtils . DF , path } ; final List < String > lines = performCommand ( cmdAttribs , 3 , timeout ) ; if ( ( lines . size ( ) ) < 2 ) { throw new IOException ( ( ( ( ( ( ( "Command<seq2seq4repair_space>line<seq2seq4repair_space>'" + ( FileSystemUtils . DF ) ) + "'<seq2seq4repair_space>did<seq2seq4repair_space>not<seq2seq4repair_space>return<seq2seq4repair_space>info<seq2seq4repair_space>as<seq2seq4repair_space>expected<seq2seq4repair_space>" ) + "for<seq2seq4repair_space>path<seq2seq4repair_space>'" ) + path ) + "'-<seq2seq4repair_space>response<seq2seq4repair_space>was<seq2seq4repair_space>" ) + lines ) ) ; } final String line2 = lines . get ( 1 ) ; StringTokenizer tok = new StringTokenizer ( line2 , "<seq2seq4repair_space>" ) ; if ( ( tok . countTokens ( ) ) < 4 ) { if ( ( ( tok . countTokens ( ) ) == 1 ) && ( ( lines . size ( ) ) >= 3 ) ) { final String line3 = lines . get ( 2 ) ; tok = new StringTokenizer ( line3 , "<seq2seq4repair_space>" ) ; } else { throw new IOException ( ( ( ( ( ( "Command<seq2seq4repair_space>line<seq2seq4repair_space>'" + ( FileSystemUtils . DF ) ) + "'<seq2seq4repair_space>did<seq2seq4repair_space>not<seq2seq4repair_space>return<seq2seq4repair_space>data<seq2seq4repair_space>as<seq2seq4repair_space>expected<seq2seq4repair_space>" ) + "for<seq2seq4repair_space>path<seq2seq4repair_space>'" ) + path ) + "'-<seq2seq4repair_space>check<seq2seq4repair_space>path<seq2seq4repair_space>is<seq2seq4repair_space>valid" ) ) ; } } else { tok . nextToken ( ) ; } tok . nextToken ( ) ; tok . nextToken ( ) ; final String freeSpace = tok . nextToken ( ) ; return parseBytes ( freeSpace , path ) ; } long parseBytes ( final String freeSpace , final String path ) throws IOException { } List < String > performCommand ( final String [ ] cmdAttribs , final int max , final long timeout ) throws IOException { } Process openProcess ( final String [ ] cmdAttribs ) throws IOException { } }

Fix:
if ( path . isEmpty ( ) ) {